Photo-rechargeable all-solid-state lithium − sulfur batteries based on perovskite indoor photovoltaic modules

Highlights

• Photo-rechargeable all-solid-state lithium − sulfur batteries is proposed based on indoor photovoltaic modules.

• The integrated unit exhibits the excellent overall energy conversion and storage efficiency.

• The device shows a new solution of energy conversion, storage and utilization.

Abstract

Photovoltaic technologies for indoor energy harvesting have attracted considerable attention because of the unique power requirements associated with the Internet of Things. However, intermittent power supplies, low light intensities, and security issues are barriers to the development of indoor photovoltaic technology. Herein, we demonstrate an all-solid-state photo-rechargeable battery system for indoor energy harvesting and storage based on an all-inorganic CsPbI₂Br perovskite solar cell module and an all-solid-state lithium − sulfur battery. This energy conversion and storage unit exhibits an excellent overall energy conversion and storage efficiency of 11.2 % under LED illumination, as well as a high electrochemical storage capacity of 1585.3 mAh g⁻¹. Moreover, the unit also shows good safety and stability after 200 h of photo-charge and galvanostatic discharge cycles due to the thermal stability of the solid-state CsPbI₂Br perovskite and sulfide electrolyte. Even in the thermal aging tests at 60°C and 90°C, the photo-rechargeable battery still delivers superior high and steady performance for 200 h.

Introduction

In recent years, indoor photovoltaics (IPVs) have been a powerful technology to convert indoor light to electric energy and satisfy the demand of the emergent Internet of Things (IoTs) and billions of self-powered devices [1], [2], [3]. Researchers have also tried to use various PV materials to absorb indoor light and fabricate IPVs. Dye-sensitized solar cells [4], [5], organic photovoltaics [6], [7], [8] and perovskite solar cells (PSCs) [9], [10] have attracted significant attention in the IPV field owing to their advantages, such as simple fabrication process, adjustable bandgap, and excellent performance. However, the intermittence and low intensities of indoor light have limited the delivery of stable power for electronics. As a viable solution, photoelectrical energy storage technology has been developed involving energy harvesting, photo-to-electricity conversion, and electrical energy transport and storage. Photo-rechargeable batteries (PRBs) are a typical photoelectrical energy storage system that can achieve simultaneous solar energy conversion and storage by combining solar cells and secondary batteries, such as lithium-ion batteries [11], [12], [13], [14], lithium–sulfur (Li−S) batteries [15] and other secondary battery systems [16], [17], [18], [19], [20]. The development of photo-rechargeable batteries provides a feasible method to harness light energy efficiently and reliably.

Although photo-rechargeable batteries have been proven to be an effective means to utilize solar energy, the conditions would be different in regard to indoor applications with intermittence and low light densities. In addition to meeting the requirements for high energy density and overall efficiency, two other factors also require special consideration when constructing indoor photo-rechargeable batteries. On the one hand, the emission spectra of indoor light sources (fluorescent lamps and light-emitting diodes (LEDs)) are located in the range of 200–700 nm, while the solar AM1.5 spectrum is approximately 300–1100 nm. Light absorbers with a wider bandgap are required to match the narrower spectrum of indoor light [10], [21], [22]. On the other hand, safety is always an important issue for electronics, especially when using devices in indoor and relatively confined spaces [23]. For indoor photo-rechargeable devices, the standard for safety should be given extra attention, and flammable liquid components should be eliminated to prevent unintentional flaming or leakage.

Herein, we propose a photo-rechargeable all-solid-state Li−S battery for indoor light harvesting and storage. The all-inorganic CsPbI₂Br PSC with an optimal bandgap achieves a high power conversion efficiency (PCE) of 30.2 % under LED illumination. Such a high PCE would be helpful for improving the overall efficiency from the original light energy to the final electric output of the whole device. Meanwhile, the all-solid-state Li−S battery with the Li₇P_2.9Sb_0.1S_10.75O_0.25 solid-state electrolyte shows high energy density and good safety, which could be an ideal choice for light energy storage and indoor applications. As a result, the photo-rechargeable unit delivers a high overall efficiency of 11.2 % under LED illuminance of 500 lux. Additionally, the integrated battery system shows satisfied safety owing to the all-inorganic and all-solid-state configuration, which could operate stably and efficiently at a high temperature of 60°C or even 90 °C. Our work shows a viable method for efficient, reliable and safe indoor light energy utilization.